A battery cell is a particularly useful article that provides stored electrical energy which can be used to energize a multitude of devices, including portable devices that require an electrical power source. A battery cell, which is often referred to, somewhat inaccurately, in an abbreviated form as a “battery,” is an electrochemical apparatus typically formed from at least one electrolyte (also referred to as an “electrolytic conductor”) disposed between a pair of spaced apart electrodes. The electrodes and electrolyte are the reactants for an electrochemical reaction that causes an electric current to flow between the electrodes when respective current collectors in contact with the electrodes are connected to an external circuit containing an object or device (generally referred to as the “load”) to be powered. The flow of electrons through the free ends of the electrodes is accompanied and caused by the creation and flow of ions in and through the electrolyte.
Typically, battery performance is enhanced by improving upon one or more of the individual components, such as the electrodes and/or electrolyte, and/or improving the interaction between or among the components of the battery. Materials that serve as electrolytes may have several different forms. For example, an electrolyte material may be a liquid, a solid, or a material such as a paste that has characteristics of both a liquid and a solid. In addition to electrodes and electrolyte, batteries may also contain a separator component, which separates the electrodes from one another. Separation of the electrodes prevents the undesirable conduction of electrons directly between the electrodes, called short circuiting. Typically, some type of solid material that is capable of creating and maintaining physical spacing between electrodes is used as a separator.
In recent years, much consideration has been given to so-called “solid-state” batteries, in which no liquids are employed in the electrodes or electrolyte. In solid-state batteries, the functions of separating electrodes (separator function) and of serving as a medium for the conduction of ions between electrodes (electrolyte function) are carried out by a single component. Thus, a solid ionically conductive electrolyte often serves as both a separator and as an electrolytic conductor. Very recently, solid ionically conductive materials, such as ionically conductive metal oxides, and amorphous ionically conductive metal oxides in particular, have been investigated for use as solid electrolytes in solid-state batteries. However, some solid ionically conductive materials have flaws, such as cracks in the material, which may adversely impact battery performance. Solid ionically conductive materials are often produced from precursors via a process that may cause cracks to be formed in the final product. Such cracks may inhibit the optimum transport of ions through the solid electrolyte. In addition, cracks may provide pathways for the transport of electrons between electrodes, thereby producing short-circuits that may cause the cell to fail. Thus, it can be appreciated that it would be useful to develop a solid ionically conductive electrolyte, suitable for use in solid-state batteries, in which flaws are sufficiently diminished or eliminated and cell performance is enhanced.
Thin film sputtered cathode materials are currently being used in state of the art thin film solid-state lithium and lithium ion batteries. Because lithium atoms generally have low diffusion coefficients in active cathode materials, the capacity of thick layer cathodes can only be shallowly, not fully, accessed during charge/discharge cycles of the battery. As a result, lithium ions can only move a limited distance from their entrance point into the cathode material at reasonable charge discharge rates. This shallow access dramatically reduces the volumetric and gravimetric energy density of the resulting batteries.
Current thin film solid-state lithium-ion battery technology employs expensive substrates, including noble metals, and uses expensive sputtering processes to form the cathode material coatings. Despite high cost, high temperature-stable noble metals, such as gold, are utilized to retain the electronic conductivity of the current collectors required in such cells under the high temperature (>850° C.) procedures used to crystallize films and/or layers of the cathode materials.
Accordingly, cost effective solid-state lithium batteries containing high capacity cathodes are highly desirable.